The C library. Stuff like fopen(3)
and kill(2)
.
The math library. Traditionally Unix systems kept stuff like sin(3)
and cos(3)
in a separate library to save space in the days before shared libraries.
The dynamic linker interface library. This is actually just a bunch of stubs that the dynamic linker replaces with pointers to its own implementation at runtime. This is where stuff like dlopen(3)
lives.
The C++ ABI support functions. The C++ compiler doesn't know how to implement thread-safe static initialization and the like, so it just calls functions that are supplied by the system. Stuff like __cxa_guard_acquire
and __cxa_pure_virtual
live here.
The dynamic linker. When you run a dynamically-linked executable, its ELF file has a DT_INTERP
entry that says “use the following program to start me”. On Android, that‘s either linker
or linker64
(depending on whether it’s a 32-bit or 64-bit executable). It's responsible for loading the ELF executable into memory and resolving references to symbols (so that when your code tries to jump to fopen(3)
, say, it lands in the right place).
The tests/
directory contains unit tests. Roughly arranged as one file per publicly-exported header file.
The benchmarks/
directory contains benchmarks.
Adding a system call usually involves:
As mentioned above, this is currently a two-step process:
This is fully automated:
If you make a change that is likely to have a wide effect on the tree (such as a libc header change), you should run make checkbuild
. A regular make
will not build the entire tree; just the minimum number of projects that are required for the device. Tests, additional developer tools, and various other modules will not be built. Note that make checkbuild
will not be complete either, as make tests
covers a few additional modules, but generally speaking make checkbuild
is enough.
The tests are all built from the tests/ directory.
$ mma $ adb sync $ adb shell /data/nativetest/bionic-unit-tests/bionic-unit-tests32 $ adb shell \ /data/nativetest/bionic-unit-tests-static/bionic-unit-tests-static32 # Only for 64-bit targets $ adb shell /data/nativetest/bionic-unit-tests/bionic-unit-tests64 $ adb shell \ /data/nativetest/bionic-unit-tests-static/bionic-unit-tests-static64
The host tests require that you have lunch
ed either an x86 or x86_64 target.
$ mma $ mm bionic-unit-tests-run-on-host32 $ mm bionic-unit-tests-run-on-host64 # For 64-bit *targets* only.
As a way to check that our tests do in fact test the correct behavior (and not just the behavior we think is correct), it is possible to run the tests against the host's glibc. The executables are already in your path.
$ mma $ bionic-unit-tests-glibc32 $ bionic-unit-tests-glibc64
For either host or target coverage, you must first:
$ export NATIVE_COVERAGE=true
bionic_coverage=true
in libc/Android.mk
and libm/Android.mk
.$ mma $ adb sync $ adb shell \ GCOV_PREFIX=/data/local/tmp/gcov \ GCOV_PREFIX_STRIP=`echo $ANDROID_BUILD_TOP | grep -o / | wc -l` \ /data/nativetest/bionic-unit-tests/bionic-unit-tests32 $ acov
acov
will pull all coverage information from the device, push it to the right directories, run lcov
, and open the coverage report in your browser.
First, build and run the host tests as usual (see above).
$ croot $ lcov -c -d $ANDROID_PRODUCT_OUT -o coverage.info $ genhtml -o covreport coverage.info # or lcov --list coverage.info
The coverage report is now available at covreport/index.html
.
This probably belongs in the NDK documentation rather than here, but these are the known ABI bugs in LP32:
time_t
is 32-bit. http://b/5819737
off_t
is 32-bit. There is off64_t
, but no _FILE_OFFSET_BITS
support. Many of the off64_t
functions are missing in older releases, and stdio uses 32-bit offsets, so there's no way to fully implement _FILE_OFFSET_BITS
.
sigset_t
is too small on ARM and x86 (but correct on MIPS), so support for real-time signals is broken. http://b/5828899